1. Field of the Invention
The present invention relates to a semiconductor device and a lead frame used for the same.
2. Description of the Related Art
To realize miniaturization and high-density packaging of the semiconductor device, a semiconductor package having plural semiconductor elements stacked and sealed in one package has already been put into practical use. In a case where priority is given to cost reduction or the like of the semiconductor package, a lead frame is used as a circuit base material where semiconductor elements are mounted. In a semiconductor package (such as TSOP) using a lead frame, plural semiconductor elements are sequentially stacked on the lead frame. The electrode pads of the semiconductor elements are electrically connected with the inner leads of the lead frame through the metal wires.
In a case where the semiconductor elements are mounted on only one side (e.g., back surface) of the lead frame, plural semiconductor elements having a one-side pad structure are stacked in a step-like fashion to electrically connect the inner leads of the lead frame and the electrode pads of the semiconductor elements via metal wires (see JP-A 2001-298150 (KOKAI), JP-A 2005-340766 (KOKAI)). The inner leads and the electrode pads are connected (wire bonded) on only a region along one side of the semiconductor element. Therefore, there is used a lead frame where the inner leads are at least partly routed via a mounting region of the semiconductor element.
Such a lead frame has plural semiconductor elements stacked on the element-mounting region where at least part of the inner leads are routed. In a case where the semiconductor elements are mounted by stacking on only one side (back surface) of the lead frame, the gaps between the inner leads routed in the element-mounting region are open upward, so that a resin used for sealing enters easily into the gaps between the inner leads. Therefore, the gaps in the inner lead portion corresponding to the element-mounting region do not cause a problem.
The semiconductor package is demanded to increase the number of semiconductor elements. Therefore, it is being studied to mount the semiconductor elements on both the top and bottom surfaces of a lead frame. But, when the semiconductor elements are mounted on both the top and bottom surfaces of the lead frame, the gaps between the inner leads are closed by the top and bottom semiconductor elements to produce an elongate space. It is hard to fill the space with the sealing resin, and the elongate space remains in the semiconductor package. If such a semiconductor package is placed under a high-humidity environment, water content absorbed into the package enters the gaps between the inner leads, and a short circuit might be caused between the inner leads by the water content.